This invention relates to water purification and more particularly it relates to a membrane water filtration system for in-home application, for example, to provide a reliable supply of safe water with only minimum maintenance.
Recent outbreaks of diseases caused by the presence of parasite cysts such as cryptosporidium and Giardia Lambia in municipal water supplies have created a great need for systems that provide potable water without fear of disease. Most municipalities rely on destruction of these pathogens with chlorine which is only partially effective. Some water purification systems use ultraviolet light disinfection but as with chlorine, this technology also is only partially effective in destroying pathogens present in water, especially the parasite cysts mentioned above.
Membrane-based technology has been used for purifying water. However, the use of conventional membranes is subject to fouling and requires frequent chemical cleaning which is not considered safe for residential or commercial use. Small disposable cartridges are sold for point-of-use applications, e.g., kitchen sink tap, but are very high cost and do not provide whole-house protection against impurities.
To improve the flow of permeate through membranes to provide purified water, different techniques have been employed. For example, U.S. Pat. No. 4,921,610 discloses removal of solids from membranes by a series of chemical cleaning cycles. The optimum time and pattern of the cleaning cycles are calculated from the rate of diminution in filtrate flow rate and the time and filtrate lost in each cycle. This is achieved by calculating from the rate of diminution of the filtrate flow rate after each application of a pressurised liquid and/or gaseous backwash cleaning cycle an equation expressing the relationship between filtrate flow and time, and, allowing for the time lost in each backwash cycle and the amount of filtrate lost in each backwash cycle, and, calculating from filtrate loss, the time loss and the relationship between filtrate flow rate and time, the optimum time of application of liquid and/or gaseous backwashes.
Japanese Patent 4-180887 discloses passing water through a hollow yarn membrane from the inside to the outside and washing the inner surface of the membrane with filtered water except during treatment times. Raw water is introduced through a top port and is filtered before being introduced to the hollow membrane and passing out a bottom port. A resin fixed bed and activated carbon are also used.
U.S. Pat. No. 4,414,113 discloses a method and apparatus for removing dissolved solids from a liquid which utilizes the technique of reverse osmosis (RO). The liquid to be treated is directed into a pressure vessel which contains a plurality of filter elements positioned therein. The filter elements have hollow RO fibers wound around foraminous center cores such that the liquid flows in a direction from the outside of the filter elements towards the center cores. The pure permeate liquid passes into the center bores of the fibers and the concentrate liquid passes into the center cores of the elements.
The method and apparatus provide for the backwashing of the filter elements when they become fouled. Further, an outer filter septum may be applied around the hollow RO fibers of the elements to remove particulate matter which would otherwise foul the hollow RO fibers.
U.S. Pat. No. 3,786,924 discloses a water purification system incorporating a reverse osmosis unit for purifying water. The system yields two streams, one of very high purity for drinking and cooking and the like and one of lower quality for use in toilet tanks, lawn watering, garden irrigation and the like. The system provides apparatus and techniques for reconciling the varying flow rates inherent in a domestic water system with the constant flow rate desirable for efficient performance of the reverse osmosis unit. Provision is made for automatic flushing and backwashing of the reverse osmosis element.
U.S. Pat. No. 3,716,141 discloses a solvent-separating apparatus for purifying water by exposing the water, under pressure, to a solvent-separating means including a non-positive displacement pump for elevating the pressure of the water prior to direction into the water-separating means and means including two presized orifices for maintaining the desired pressure and desired flow rate of the water through the water-separating means and for flushing the water-separating means periodically without the necessity of further adjustments in order to return the system to normal operating conditions.
U.S. Pat. No. 3,992,301 discloses an automatic flushing and cleaning system for membrane separation machines such as reverse osmosis machines having plural modules or membranes. Cleaning may be by way of reducing the pressure to allow the membrane to relax, by the injection of air or inert gas to provide turbulence, and/or by injection of flushing liquid which may include chemical cleaning additives. Pumps, automatic valving, and pressure controls are provided, along with a complete time operated electrical sequencing system whereby desired purging, flushing and cleaning cycles are automatically undertaken at periodic intervals or in response to one or more preferred conditions.
U.S. Pat. No. 4,876,000 discloses a hollow fiber filter device having a filter casing which is partitioned by a horizontal member into a filtered liquid chamber and a filtering chamber and a plurality of filter modules are suspended downwardly from the horizontal member. Each of the modules includes a plurality of hollow fibers having upper ends open to the filtered liquid chamber and also having lower ends open to a liquid-collecting chamber which is sealed from the filtering chamber and is arranged to communicate with the filtered liquid chamber by way of a conduit so that the full length of the fiber is utilized for filtration.
U.S. Pat. No. 5,437,788 discloses a filter assembly which includes a housing divided into a first chamber and a second chamber. A filter element is disposed in the first chamber, and a conduit is disposed in and opens to the second chamber. A weep hole introduces a backwash liquid from the second chamber into the filter element or the conduit. A differential pressure is then established between the opening in the conduit and the exterior of the filter element to force the backwash liquid through the filter element and thereby clean the filter element and/or strip a precoat layer from the filter element.
U.S. Pat. No. 5,053,128 discloses a method of manufacturing a diffusion and/or filtration apparatus, including a housing consisting of a cylindrical open-ended main part closed by two end caps and being provided with an inlet and outlet for a first fluid and at least one outlet for a second fluid, said first fluid being adapted to flow through the fibers of a bundle of semi-permeable hollow fibers arranged between two end walls within the housing and said second fluid being adapted to be removed from the space outside the fibers through said at least one outlet for the second fluid.
U.S. Pat. No. 5,059,374 discloses a process for sealing a hollow fiber membrane separation module into a case.
U.S. Pat. No. 5,160,042 discloses an annular double ended hollow fiber bundle, a fluid separation apparatus comprising the annular double ended hollow fiber bundle having bores open at both ends of the hollow fibers embedded in the two tube-sheets enclosed in a shell having multiple ports, a fluid entrance port, a non-permeate exit port and at least one permeate exit port, wherein said double ended hollow fiber bundle is encased in an essentially impermeable film barrier except for entrance regions situated in selected areas between the tubesheets and to processes for separating fluids mixtures.
In spite of these disclosures, there is still a great need for membrane-based filtration system suitable for in-home, commercial and institutional applications. That is, there is great need for a membrane filtration system that will provide reliable, safe service for the house or institution for substantial periods of time without cleaning, in a cost-effective manner.
It is an object of this invention to provide a membrane-based filtration system suitable for in-home use.
It is another object of this invention to provide a hollow fiber membrane-based filtration system suitable for removing parasite cysts such as cryptosporidium and Giardia Lambia bacteria such as E-coli and viruses from municipal waters to provide safe drinking water.
Yet, it is another object of the invention to provide an improved method for purifying municipal water for drinking purposes employing membrane-based filtration wherein cleaning of the membrane is facilitated to improve flux.
And still, it is another object of the invention to provide an improved method for purifying municipal water of cysts, for example, using microfiltration or ultrafiltration hollow fiber membranes to provide for improved recovery.
And still further, it is an object of this invention to provide an improved method for purifying municipal water using microfiltration or ultrafiltration hollow fiber membranes to provide safe drinking water for entire households in a cost-effective manner for substantial periods of time without cleaning the membranes.
These and other objects will become apparent from a reading of the specification, claims and drawings appended hereto.
In accordance with these objects, there is provided a method of purifying feedwater to remove impurities including suspended solids therefrom, the method suitable for using water in-line pressure to permeate water through membranes and to backflush the membranes to remove solids collected or deposited thereon. The method comprises providing a chamber defined by a wall having an inside and having a first end and a second end. Membranes such as hollow fiber membranes selected from ultrafiltration and microfiltration membranes extend between the first end or region and the second end or region. A feedwater entrance is adapted for connection to a water line to introduce feedwater to the chamber at in-line pressure. A permeate water exit is provided for directing purified water throughout the building. In the method, feedwater is introduced through the entrance to the chamber or module to the outside membranes such as hollow fiber membranes. The feedwater is filtered in the chamber by using the in-line pressure to pass water through the hollow fiber membranes to provide permeate water inside the hollow fiber membranes and to concentrate suspended solids outside or on the shell side of the hollow fiber membranes to provide concentrate water. The permeate water flows down the lumens of the hollow fiber membranes and is collected in a permeate collector and dispensed for use. A portion of the permeate water is directed to a diaphragm tank which collects permeate water under water line pressure, the diaphragm tank in liquid connection with the permeate collector. Periodically, the chamber or module is flushed with feedwater and simultaneously therewith the hollow fiber membranes are backflushed with permeate water from the diaphragm tank to remove solids from the membranes while continuing to pass feedwater through the chamber to flush the concentrate water containing solids from the chamber to a drain.
A system is provided for purifying feedwater to remove impurities including solids therefrom, the system adapted to use in-line water pressure to permeate water through membranes and to remove solids collected thereon. The system comprises a chamber having a first end and a second end, a feedwater entrance in said chamber for connecting to a feedwater line and, a permeate water exit and a concentrate water exit. The chamber contains membranes such as hollow fiber membranes selected from ultrafiltration and microfiltration membranes provided in said chamber and disposed between the first end and the second end, the hollow fiber membranes in fluid communication with said permeate water exit and adapted for permeating water from said chamber therethrough into lumens thereof to purify water and reject solids under in-line water pressure to provide concentrate water in said chamber. A permeate water collector is provided for removal of permeate water from said lumens for re-distribution. A diaphragm tank is provided in liquid communication with said permeate water collector for storing permeate water at in-line water pressure for backwashing the membranes with permeate water. Valve means is used for periodically removing concentrate water from said chamber through the concentrate water exit and for lowering the pressure in the chamber below in-line water pressure, said valve means by removing concentrate water and lowering the pressure in said chamber (i) activating backwashing of said membranes with permeate water from said diaphragm tank to dislodge solids from said membranes for removal with said concentrate water during said draining, and (ii) activating flushing of said chamber with feedwater during said periodic flushing and backwashing. The system may be manually drained by opening the drain valve or the system may be manually drained and backwashed by closing the water inlet valve and opening the drain valve.